chemistry/math solution stoichiometry

A 9.3 gram sample of chromium (III) nitrate is placed in 30.0 mL of a 0.100 M (molarity) barium hydroxide solution. What is the molarity of the chromium (III) nitrate solution before the reaction occurred?

Actually you don't need . We don't even need the reaction because we don't even consider it.

You want the molarity (i.e. # of moles divided by volume) of chromium (III) nitrate. We're given that they're 9.3 grams of it (which can be converted into moles) and we're given that it's put into a 30 mL solution.

No for the first question, yes for the second. The 2 in front of means that 2 of chromium (III) nitrate is needed for it to react with the barium hydroxide. It has nothing to do with its molar mass, only the subscripts of the compound give you that information.